Avoiding SDH implementations
Posted by Ivan on January 10, 2006
Most of existing telecom operators insist in implementing SDH equipment in their networks. Considering some of them have Metro Ethernet as well as IP/MPLS platforms, what is the right argument -to them- for implementing only DWDM and Optical ethernet instead of SDH combined with DWDM? Under what considerations is still needed SDH?
Many telecom operators have an extensive investment in SONET/SDH transmission equipment, along with automated operations support systems. Any service that can be carried over SONET, by adding a card to one of their existing pieces of equipment, is easy to provide to virtually all their customers served by SONET equipment. An additional benefit of a SONET platform is the excellent management visibility it provides, and the fast protection mechanisms it supports. The service provider can be sure the service is meeting service level agreements.
Where SONET falls short is in the provisioning of high bandwidth Ethernet services. For services such as Gigabit Ethernet, the bandwidth is a large fraction of the bandwidth of a SONET platform in most deployed networks, and it is less likely that existing equipment will have the free capacity to support it. If one has to install a new piece of SONET equipment to carry a Gigabit Ethernet service, the equipment cost is quite high. For high bandwidth Ethernet services, a combined OTN/DWDM platform is much more cost effective. The OTN is the ITU standard aimed at Optical Transport Networks. It is simpler to implement than SONET, and as part of a DWDM system, is much more scalable than the typical SONET add/drop multiplexers found in carrier networks. OTN has the same powerful management functionality as SONET, and the same protection switching capabilities.
One can use DWDM without OTN as well. What you would have to be careful of is that the equipment provided sufficient management visibility to serve as a satisfactory service delivery platform. Ciena has products that meet this need, even without OTN. The IEEE has formulated standards for link management of native Ethernet links, but these are not yet widely deployed.
